Snow Depth but No Depth on Landing

Snow is on my mind. My snow blower has been in daily use for weeks here on the eastern shore of Lake Michigan. My airport, Muskegon County, has recorded more than 90 inches of snowfall so far this winter. That is close to the seasonal average and there are weeks of winter to go.

Flying in the snow is a huge risk for VFR because snow, even moderate snow, cuts visibility to almost nothing. You may as well be inside a cloud as to fly into a snow shower. Unless you’re flying an airplane with automatic landing capability snow reduced visibility is a big problem under IFR, too, because you still have to see to land at the end of the instrument approach.

But most of the hassle of flying in snow is on the ground. The taxiways and runways have to be cleared. With the kind of snow we’ve had this year the snow banks on either side of the taxiways become an issue, especially for low wing airplanes, because the snow piles become higher than the underside of the wing tips.

And then there is the ice that packed snow becomes on pavement. Except for turboprops with their flat pitch “beta” propeller setting it’s impossible to get rid of all of the thrust of an idling engine. Once an airplane starts to slide—with wind gusts often pitching in to add to the fun—we pilots are pretty much along for the ride until the tires find some grip, if they do before you hit the snow bank.

It snows a lot here on the downwind shore of Lake Michigan so my airport is prepared. The maintenance guys have superb equipment and they work long hours. At least one runway is always operational, the taxiways available, and by 7 or so in the morning the T-hangar apron and taxiways are cleared.

But this winter has been so windy clearing the falling snow is not even half the battle because the wind just picks up the snow and moves it back over the pavement. Airports need lots of open space so we don’t have obstructions to avoid and that space gives the wind lots of distance to do its snow moving work. What looks like even a small drift sends the airplane turning toward the drift when one of the main tires hits the drift before the other. Taxiing can be an adventure.

I’ve spent way too much time flying in snow country during the winter but only twice have encountered the absolutely smooth snow cover that destroys all depth perception. It doesn’t happen often, but is a strange and even scary experience on landing.

The first time I encountered the “glassy” snow cover on landing was at Kirksville, Missouri several years ago. I descended out of the clouds into good visibility on the approach to see nothing but white ahead. It was morning, it had snowed overnight, and there was no wind. The snow cover was absolutely uniform and smooth.

The localizer was centered so I knew the was runway straight ahead. I had no way of knowing how deep the snow was because there was no weather reporting on the field and nobody on Unicom. There was not a tire track or windblown ripple on the surface of the snow. The runway is 100 feet wide, and long and I could see some of the edge light stanchions sticking up through the snow. As I descended close to the runway my depth perception evaporated. I didn’t know if I was 10 feet in the air or 10 inches.

I raised the nose, reduced the power a little, and hoped. The airplane settled softly into the snow which turned out to be only about three inches deep. The soft snow cushioned the touchdown but when the wheels actually touched the snow came as a surprise to me.

What I had experienced is the same phenomenon as landing on perfectly smooth glassy water in a floatplane. Our eyes and brain need texture to judge distance. When a surface is perfectly uniform there is no texture and our senses go tilt. The people who design visual displays for simulators learned this many years ago. If the sim shows you a uniform and smooth runway we can’t judge our height. But if there are expansion cracks in the pavement, or a little rough appearance to the surface, we can make decent landings.

The only other time I have experienced the “glassy snow” was landing at Oshkosh on Runway 27 one morning last winter. Again, there was not a single track or tiny drift on the snow, but this time I knew what to expect. I simply held a steady descent rate and nose-up attitude and waited for the wheels to find the surface of the snow.

Being the first to land on perfectly smooth snow is quite an experience, and one I don’t expect to have this winter. It’s blowing more than 30 knots out there again today—and snowing sideways.

4 Responses to Snow Depth but No Depth on Landing

That’s classic. As a former ski instructor I know all about the joys of making “first tracks” on a sunny powder morning. Never thought about how fun that could be on a snowy runway. Down here in Atlanta I doubt I’ll ever get that chance, but thanks, Mac, for bringing back those happy memories from my mountain days.

I had my first one of those in Boston, in a MD-88! Hand flown to a couple hundred feet (weather reported around 800….), broke out and could only see bumps where the landing lights were. Flight director, g/s, loc all centered up perfectly, which was the only comfort I really had. Waited for bitching Betty to say 30′ when I snatched her to idle, at 10′ I raised the nose. Few seconds later the spoilers deployed, my first indication I was on the ground. Smoothest touchdown I ever had in one of those! It’s PURE instrument flying. Now, when tower told us to take taxiway Quebec, we had to cry uncle and ask for progressives, couldn’t see a THING on the ground.

We said we were gonna divert if they didn’t start us on an approach immediately. So they put us on the approach. We were holding for runway clearing, apparently a different runway… Had to cross reference the localizer on rollout. It was THAT bad.

Have a lot of time over the ocean in S-3B Vikings, both high and very low in all sorts of weather. When the water is smooth, 10,000 feet looks NO DIFFERENT than 100 feet. The Persian gulf is like that. In summer, perfectly smooth, and because of the natural gas burning, temperature inversion and generally dirty air, vis in never more than a few miles. I logged every hour I flew over that gulf as instrument time. Vertigo was a way of life. Night formation flight in that goo was better than an amusement park ride!

I’m not sure how to advise light civil pilots how to cope with it, I ALWAYS had TONS of proficiency, advanced equipment and other professionals with me. It’s difficult to know, without experience, that you don’t have the experience to handle it. Just because it’s legal, doesn’t mean it’s safe. I guess I would say to seek out conditions like it and go with someone who IS proficient with it. It’s about the only way to get some experience like that, safely. Then you can make a better decision at go time.

I’ve landed on beau coup snowy runways over the years, but the only time I can recall being first to land on an untrammeled runway was at Greybull, WY, on a cold morning in the winter of 1980, in our TR182. At that time, Greybull’s only instrument approach was the NDB off to the west side of the ramp with the runway to the east of the ramp and 1400′ AGL MDA, but the bases were high, and below the clouds the visibility was well over 10 miles, so the approach was easy. But in spite of the great visibility, it was very hard to make out the runway–nice level snow, although as I got closer, I could make out the edges of it–it helped that I’d been there before.

When I called Unicom, I asked for the snow depth, and she told me that it was “only a couple of inches”. I decided that a very soft, nose high, power on, feel for the ground sort of landing was necessary, and it was nearly impossible to tell when touchdown occurred. I guess that’s what you’re referring to as a glassy water landing.

The snow was a little deeper than “a couple inches”, maybe 3″-4″ in places, because it took a bit of power to taxi. As I taxied past where I’d touched down, it was interesting to see the mains’ marks, and then some 100′ or so farther down, the nose tire’s mark.

I’ve never done any ski-flying, but I think that landing gave me a feel for the joy that pilots describe when they land in some snowy field where no one has been before. It’s another part of why winter flying is so special–snow covers up so many “uglies”.